Differing opinions have been expressed on the taxonomic standing of Fissidens arcticus. According to W. C. Steere (1978), it might be only an environmentally induced expression of F. bryoides, but A. A. Frisvoll (1981), who reported the species from Svalbard, suggested that it be treated as a subspecies or variety of F. bryoides. They and other previous workers (Steere and G. R. Brassard 1974; M. A. Bruggeman-Nannenga and E. Nyholm 1986), however, did not mention the dimorphic stems, of which the fertile (perichaetial) ones are shorter and have fewer pairs of leaves than the infertile ones. That character and the tendency of the limbidium to be expressed on all laminae of the leaves of perichaetial stems but otherwise restricted to the vaginant lamina of infertile stems distinguish F. arcticus.